In a conventional electrical discharge machine, a working electrode and a workpiece are spaced at a predetermined gap and a pulse-like voltage is applied between the electrode and the workpiece while supplying a working fluid in the gap, thereby causing an electrical discharge to perform the spark erosion.
In such well-known conventional electrical discharge machine, in order to prevent a short circuit and an abnormal arc discharge or the like from occurring between the electrode and the workpiece during the working operation, a servo motion of the workpiece and the electrode is additionally performed to automatically adjust the width of the working gap in response to pollution of the working fluid in the working gap and to a change in a discharge current or the like, in addition to the relative work-movement between the workpiece and the electrode. However, when the working speed (g/min) substantially drops or the electrode is excessively worn, the conventional electrical discharge machine described above cannot cope with these conditions. Thus, there are problems in that the working operation stops and sufficient work accuracy cannot be obtained. Effective means for eliminating such problems has not yet been proposed.